The present invention relates generally to communications systems, and more specifically to a battery saving system for a battery-powered communications system such as TDM (time division multiplex) radio communications system connected to a public or private switched telephone network.
A battery-powered communications system such as TDM radio communications system is known in the art of telephone switching as a means for connecting remotely located telephone subscribers to the public switched telephone network. The system includes a base station connected to the network and remote terminal stations to which subscriber telephones are connected. Depending on the distances between the base station and terminal stations, one or more regenerative repeater stations are located for relaying signals. Because of the scarsity of electric energy source, both repeater and terminal stations use a solar battery for charging a storage battery for operation. Synchronized battery saving techniques have evolved from this background by periodically interrupting the power supplies of the repeater stations in response to a battery-saving command signal sent at constant intervals from the base station during a standby mode. This signal is relayed from one repeater station to the next or to the terminal stations to synchronously cut off the power-drain units of the repeater and terminal stations. As described in U.S. Pat. No. 4,577,315, issued to S. Otsuka, battery saving operation is usually continued even if a call request occurs in a standby mode by exchanging call-setup signals during available time intervals. In addition, from the power savings viewpoint, it is desirable to increase the ratio of power-off to power-on times. However, if the ratio is too high, the available time intervals for exchanging call-setup signals are not sufficient for handling simultaneous calls, and hence contention is likely to occur between call requests, resulting in a queue, or long time to establish a connection.